Project Summary Despite the higher prevalence of low back pain (LBP) among persons with unilateral lower limb amputation (ULLA) compared to able-bodied individuals, relatively little is known about the fundamental mechanisms underlying this condition. Our research represents a first step toward investigating lower back biomechanics using advanced computational modeling techniques to inform the future design of effective interventions for LBP. Specifically, the impact of trunk neuromuscular patterns adopted by persons with ULLA while performing activities of daily living on spinal loads and the risk of spinal tissue damage will be investigated. This will be achieved via secondary biomechanical analyses of a large set of high-quality kinematics data obtained from individuals with and without ULLA performing the following tasks: 1) walking at self-selected and controlled speeds, 2) sit-to-stand and stand-to-sit, and 3) stairs-up and stairs-down. Our central hypothesis is that, compared to able-bodied individuals, trunk movement strategies adopted by persons with ULLA to cope with physical demands of common daily activities are associated with a complex pattern of internal muscle forces that result in larger loads on the spine and a higher probability for spinal tissue damage. Our dataset draws from the Biomechanics Laboratory at Walter Reed National Military Medical Center (WRNMMC) which has unprecedented access to a large population of service members with ULLA. Using this unique database, we will implement our novel finite element modeling approach to estimate the internal muscle forces (i.e., adopted neuromuscular patterns) needed to perform daily physical activities on the basis of satisfying equilibrium and stability across the entire lumbar spine. Completion of this project will enable us to determine differences in muscle recruitment, as well as the resultant effects on spinal loads and the risk of spinal tissue damage, between persons with and without ULLA. Hence, this pilot project is expected to establish the initial groundwork for future research involving the design of highly specific interventions aimed at trunk neuromuscular behaviors during post-amputation rehabilitation to lessen adverse effects on lower back biomechanics and the potential for LBP.